1. Field of the Invention
The present invention relates to a cleaning apparatus, an image forming apparatus and a cleaning method.
2. Description of Related Art
As an electrophotographic image forming apparatus, for example, there has been conventionally an intermediate transfer type image forming apparatus which forms toner images of Y (yellow), M (magenta), C (cyan) and K (black) on separate photoreceptor drums, primarily transfers the toner images of respective Y, M, C and K colors formed on the respective photoreceptor drums onto a rotating intermediate transfer belt so as to be superposed on each other and thereafter secondarily transfers the respective superposed toner images transferred on the intermediate transfer belt onto a sheet of paper.
The intermediate transfer belt formed of a resin material such as polyimide and polyphenylene sulfide is generally and widely used. However, due to the microscopic irregularities in surface shape of paper to be used (for example, plain paper, thin coated paper and board paper), the contact between an intermediate transfer belt and a sheet at the secondary transfer position is lowered, and thus it is difficult to ensure the transfer property in some cases.
In order to prevent such decrease in transfer property, there is an intermediate transfer belt which has an elastic layer of rubber material or the like on a substrate layer formed of a resin material (see Japanese Patent Application Laid Open Publication No. 2011-107534). The elastic layer enables the intermediate transfer belt to have the surface shape deformed so as to fit the surface shape of sheet, and thus improves the contact between the intermediate transfer belt and the sheet.
It is desired that all toner images are transferred onto a sheet when transferring the toner images on an intermediate transfer belt onto the sheet. However, there are actually cases where a part of the toner particles are not transferred and remain on the intermediate transfer belt. There are also cases where paper powders are attached to the intermediate transfer belt due to the contact between the sheet and the intermediate transfer belt. If such residues of residual toners and paper powders remain attached to the intermediate transfer belt, the formation of toner images thereafter is disturbed. Thus, the image forming apparatus is provided with a cleaning apparatus which removes residues on the intermediate transfer belt.
The cleaning apparatus generally has a configuration of scraping and removing the residues on the intermediate transfer belt by making the tip of a cleaning blade formed of an elastic body such as urethane rubber come into contact with the rotating intermediate transfer belt. However, when the intermediate transfer belt has an elastic layer, the elastic bodies of the intermediate transfer belt and the cleaning blade contact each other, which may turn the blade by the torque increase. Thus, there is also used a cleaning apparatus which applies a cleaning blade formed of a thin metal piece (see Japanese Patent Application Laid Open Publication No. H4-352186).
However, even in the cleaning blade made of metal, the tip thereof is gradually worn away while cleaning the residues such as residual toners and paper powders on the intermediate transfer belt over a long period, which makes it difficult to appropriately remove the residues in some cases. Furthermore, the intermediate transfer belt having an elastic layer has a problem that the belt surface is hardened with its use.
In a case where a cleaning blade made of metal contacts the intermediate transfer belt having an elastic layer, the cleaning blade is pressed down into the belt surface while the intermediate transfer belt is soft (see FIG. 5). However, as the intermediate transfer belt becomes harder, the pressing down of cleaning blade into the belt surface is reduced. Thus, the angle (edge angle) between the intermediate transfer belt and the cleaning blade is possibly changed and causes a cleaning defect such as a vertical line and an uncleaned part in some cases.